1. Field of the Invention
The present invention relates to an active type distance measurement device for measuring distances to a plurality of distance measurement view fields to be used in a camera having an auto-focusing function.
2. Description of the Related Art
Referring to FIG. 8, in a prior art distance measurement device having a plurality of distance measurement view fields, light projected from a plurality of light emitting devices 1, 2 and 3 are projected to objects 5, 6 and 7 through a projection lens 4 and the lights reflected by the objects 5, 6 and 7 are focused on a plurality of two-split silicon photo-cells (SPC) through a focusing lens 8. Numeral 12 denotes a camera body which includes the distance measurement device. The two-split SPC's 9, 10 and 11 are formed by SPC's 9F, 10F and 11F which are closer to the light emitting devices and SPC's 9N, 10N and 11N on the opposite side, as shown in FIG. 9A, projection light images on the two-split SPC's when distances to the objects are 6 meters, 1.2 meters and 0.6 meter, respectively, are shown by 9B, 10B and 11B in FIG. 9B and 9C, 10C and 11C in FIG. 9C, and ratios of light images on 9F and 9N, 10F and 10N, and 11F and 11N are calculated to determine the distances to the objects 5, 6 and 7.
However, in the prior art camera, when the object is at an extremely near distance such as at approximately 0.2 meter, a center of gravity of the projected image is actually moved to a near end as shown by 10E in FIG. 10, but because of large defocusing of the image, a ratio of the incident lights to 10F and 10N on the two-split SPC 10 is apparently closer to the far end than that of the projected image 10D obtained when the distance is 0.6 meter, and an error in the distance measurement appears.
In a camera having one distance measurement view field rather than a plurality of distance measurement view fields, a sensor for measuring an extremely near distance may be separately provided. However, in the camera for measuring the distances to the plurality of view fields, there is no space to separately arrange a sensor for measuring the extremely near distance because the two-split SPC 11 is located adjacent to the two-split SPC 10. Even if there is a space, another sensor and an associated circuit are required in a large scale circuit required for the measurement of the distances to the plurality of view fields.